Developments in real estate in the Washington area:

* The architectural firm of Hellmuth, Obata & Kassabaum has signed a long-term lease for approximately 12,000 square feet of space at 1110 Vermont Ave. NW. Upon commencement of this lease, the building will be fully occupied.

* Fox Distribution Inc., a public warehousing and delivery service, has leased 95,000 square feet of space at 8242 Sandy Court in the Baltimore-Washington Industrial Park in Jessup, Md.

* The John Ray for Mayor campaign has leased 12,000 square feet of space for its campaign headquarters at 501 13th St. NW.

* Dames & Moore, an environmental and applied earth sciences consulting firm, has leased an additional 1,834 square feet for its offices at 7101 Wisconsin Ave. NW.

* Cambridge Survey Research Inc., a political polling company, has leased 2,245 square feet at 1750 Pennsylvania Ave. NW.

* Lincoln Property Co. SW Inc., a commercial real estate development company with offices in 26 cities, has leased 1,216 square feet at 2000 L St. NW.

* The Specialized Carriers and Rigging Association has been subleased 3,000 square feet at 733 15th St. NW.

Mistral Co. Inc. has leased 29,000 square feet of space in the Parkway Business Center at 7222 Parkway Drive in Dorsey, Md.

* The law firm of Williams & Connolly has leased 9,300 square feet in the Barr Building at 917 17th St. NW.

* ACA America Inc. has leased 9,069 square feet in the Dominion Bank Building at 206 N. Washington St. in Alexandria.

* Sullivan and Co. Ltd., an accounting firm, has purchased 4,700 square feet of space in the Sunset Office Condominiums at 11311 Sunset Hills Road in Reston.

* The Pavilion on the Park apartment building at 5340 Holmes Run Parkway in Alexandria has been sold to Alexandria Development Co. for $8.7 million.

* Pan American World Airways has leased space for its middle Atlantic regional sales office in the McLean Professional Park on Chain Bridge Road.

* The Northern Virginia Planning District Commission has leased office space in the Suburban II Building on Little River Turnpike in Annandale.

* Delta Communications Inc. has leased 5,000 square feet of space in the Oakland Ridge Industrial Park at 9121-B Red Branch Road in Columbia.

* The law firm of Gimmel, Weiman & Savits has relocated to about 5,000 square feet of space in the Lake Forest Professional Building at 444 North Frederick Ave. in Gaithersburg.

* The Baltimore-based law firm Venable, Baetjer, Howard and Civiletti has leased an additional 5,937 square feet for its Washington office at 1301 Pennsylvania Ave. NW.

* The real estate investment firm North American Developments has leased 1,178 square feet at 734 15th St. NW